1. Field of the Invention
The present invention relates generally to gas turbine engines and, more particularly, to an improved cowl structure for use in the combustion chamber of a gas turbine engine.
2. Description of Related Art
In a gas turbine engine, pressurized air is provided from the compressor stage to the combustor, whereupon it is mixed with fuel and is burned in the combustion chamber. The amount of pressurized air which enters the fuel/air mixes, and correspondingly the inner and outer passages of the combustor, has typically been regulated by inner and outer cowls located upstream of the fuel/air mixers and the combustor dome. Such cowls have been generally held in place by means of a bolted joint which includes the combustor dome, the cowl, and either the inner outer combustor liner. Accordingly, both the outer and inner cowls of a gas turbine engine experience a slight change in pressure thereacross, as well as a vibratory load induced by the engine. While these environmental factors have a greater effect on the outer cowl, they nevertheless cause wear on both cowls which consequently limit the life thereof.
In addressing this problem, the prior art has generally taken one of two approaches. The first of which involves use of a sheet metal body for the cowls with a lip formed at the leading edge thereof, preferably by curling or wrapping the sheet metal around a damper wire. However, it has been found that this design is life-limited due to a rubbing-type wear occurring at the interface of the wire and the sheet metal body. One attempt to circumvent this rubbing wear problem is disclosed in U.S. Pat. No. 5,181,377 to Napoli et al., where a two-ply, laminate configuration is described. Besides having to maintain the structural integrity of this two-ply configuration, however, another concern with the lip disclosed therein is the structural integrity for vibration damping under a variety of operating conditions.
Still another cowl design involves a machined ring which forms the leading edge lip of the cowl, where the ring is welded to a formed sheet metal body. Such a machined ring provides a solid lip for the cowl, which is desirable, but circumferential welding thereof to the formed sheet metal body has resulted in stress concentrations both in and around the weld which are sources of failure initiation of the cowl.
Accordingly, it would be desirable for a cowl structure to be developed for the combustor of a gas turbine engine which provides not only a solid lip at the leading edge thereof, but also has the structural integrity to significantly increase the life of the cowl. Moreover, it would be advantageous for such a cowl to eliminate all rubbing wear while performing its vibratory damping function.